Solid-state imaging device and electronic apparatus

ABSTRACT

A solid-state imaging device includes: an R pixel provided with an R filter for transmitting red-color light; a B pixel provided with a B filter for transmitting blue-color light; an S1 pixel which is provided with an S1 filter with a visible light transmittance independent of wavelengths in a visible light region and has a sensitivity higher than that of the R pixel; and an S2 pixel which is provided with an S2 filter with a visible light transmittance independent of wavelengths in the visible light region and lower than the visible light transmittance of the S1 filter and has a sensitivity lower than the sensitivity of the S1 pixel.

The subject matter of U.S. application Ser. No. 12/850,347 isincorporated herein by reference. The present application is acontinuation of U.S. Ser. No. 12/850,347, filed Aug. 4, 2010, whichclaims priority to Japanese Patent Application JP 2009-214819 filed inthe Japanese Patent Office on Sep. 16, 2009, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state imaging device employinga filter and relates to an electronic apparatus such as a digital-stillcamera and a video camera which employ the solid-state imaging device.

2. Description of the Related Art

In recent years, the miniaturization of the size of a pixel used in asolid-state imaging device has been making progress in order to allowthe number of pixels used in the solid-state imaging device to beincreased. Accompanying the miniaturization of the size of the pixel, anarea occupied by the pixel also decreases so that the quantity of lightincident on the pixel also becomes smaller as well. In addition, sincean area occupied by a photodiode employed in the pixel also becomesnarrow, the number of photons accumulated in the photodiode also becomessmaller as well and sensitivity deteriorates. Thus, the magnitude of asaturated signal generated in a saturated state of the pixel decreasesas well. The sensitivity of a pixel employed in a solid-state imagetaking device is defined as the ratio of the magnitude of a signalgenerated by the pixel due to light incident on the pixel to thequantity of the incident light as will be explained later by referringto a diagram of FIG. 4. A high sensitivity of a pixel employed in asolid-state image taking device gives rise to a decrease in dynamicrange as will be described later by referring to diagrams of FIGS. 4 and9. That is to say, a high ratio of the magnitude of a signal generatedby a pixel due light incident on the pixel to the quantity of theincident light results in a decrease in dynamic range.

In general, in comparison with a camera making use of a silver saltfilm, a digital-still or video camera employing a solid-state imagingdevice has a narrow dynamic range. The dynamic range is a brightnessrange in which an image can be taken without causing white and blackfailures. However, a monitoring camera is demanded to be capable oftaking an image throughout a range from a dark place to a bright place.In addition, a monitoring camera is even demanded to be also capable oftaking an image also at a dark place without causing a failure.

The dynamic range of a camera employing a solid-state imaging device isnormally determined by a pixel which has the highest sensitivity. In acamera employing a solid-state imaging device having filters ofelementary colors such as the G (green), R (red) and B (blue) colors forexample, the dynamic range D of the G (green) pixel having the highestsensitivity normally determines the dynamic range of the camera. In thecase of a solid-state imaging device having a saturated signal magnitudewhich is uniform for all pixels, a pixel having a highest sensitivity isthe first pixel with its output signal attaining the magnitude of thesaturated signal at an earliest time. This is because the pixel havingthe highest sensitivity is a pixel with a filter having the highesttransmittance (that is, a filter transmitting a largest quantity oflight) so that a largest number of protons are accumulated in a photodiode included in the pixel, causing a signal output by the pixel toattain the magnitude of the saturated signal at an earliest time.

There has been proposed a existing technology for improving thesensitivity of the solid-state imaging device. In accordance with theproposed existing technology, GRB (Green, Read and Blue) pixels of aBayer array including a layout of filters of elementary colors (that is,the GRB colors) are used as pixels of a YRB array by making use of a Ypixel including a filter not absorbing light with visible wavelengths asa substitute for the G pixel. In addition, there has also been proposedanother existing technology for improving the sensitivity of thesolid-state imaging device. In accordance with the other proposedexisting technology, one of G pixels placed in a checker board state inthe Bayer array is replaced by the Y pixel described above. For moreinformation on the existing technologies for improving the sensitivityof the solid-state imaging device, the reader is advised to refer todocuments such as Japanese Patent Laid-open No. 2008-205940.

In the mean time, there has been proposed a existing technology forwidening the dynamic range. In accordance with this proposed existingtechnology, two images are synthesized. The two images are ahigh-sensitivity image and a low-sensitivity image which have brightnesslevels different from each other. For more information on the existingtechnology for widening the dynamic range, the reader is advised torefer to documents such as Japanese Patent Laid-open No. 2004-56568.

SUMMARY OF THE INVENTION

For the same output-signal magnitude, however, the quantity of lightincident on a photodiode in each of the aforementioned Y pixelsincluding a layout of filters not absorbing light at visible wavelengthsis smaller than the quantity of light incident on a photodiode in eachof the GRB pixels.

To put it in detail, the quantity of light incident on a pixel isrepresented by the horizontal axis whereas the magnitude of anelectrical signal generated by the pixel is represented by the verticalaxis. As shown in the diagram of FIG. 9, the Y pixel attains asaturation point at an incident light quantity smaller than those of theGRB pixels. Thus, the dynamic range D (Y) of a solid-state imagingdevice employing Y pixels is narrower than the dynamic range D of asolid-state imaging device employing ordinary GRB pixels.

The dynamic range D (Y) of a solid-state imaging device employing Ypixels can be widened by suppressing the quantity of light incident oneach of the Y pixels. If the quantity of light incident on each of the Ypixels is suppressed, however, the magnitude of a signal output by eachof the Y pixels decreases so that the sensitivity of the solid-stateimaging device employing the Y pixels deteriorates.

In addition, in accordance with the existing technology proposed as atechnology for widening, two images are synthesized. The two images area high-sensitivity image and a low-sensitivity image which havebrightness levels different from each other. It is thus necessary toacquire the two images as a high-sensitivity image and a low-sensitivityimage which have brightness levels different from each other. As amethod for acquiring the two images as a high-sensitivity image and alow-sensitivity image which have brightness levels different from eachother, it is possible to typically make use of two cameras withdifferent sensitivities or one camera in two different exposureoperations obtained by changing the exposure time.

If two cameras with different sensitivities are used, however, imagesmust be taken by aligning the two cameras. Thus, the positions of thetwo images to be taken are shifted from each other. In addition, inaccordance with the method of making use of one camera in two differentexposure operations obtained by changing the exposure time, the twodifferent exposure operations are carried out so that a time differenceis generated between the two images.

On top of that, there have been also proposed a solid-state imagingdevice employing pixels with different sensitivities and a solid-stateimaging device having every pixel provided with an embeddedhigh-sensitivity sensor as well as an embedded low-sensitivity sensor.However, it is difficult to carry out a stable process of manufacturingthese solid-state imaging devices which include low-sensitivity pixelsand high-sensitivity pixels. In addition, due to the complicatedstructures of the solid-state imaging devices, it is difficult to keepup with smaller pixel sizes.

Addressing the problems described above, inventors of embodiments of thepresent invention have presented a solid-state imaging device which iscapable of keeping up with smaller pixel sizes and increasing thesensitivity as well as the dynamic range.

A solid-state imaging device provided by embodiments of the presentinvention has an R pixel provided with an R filter for transmittingred-color light and a B pixel provided with a B filter for transmittingblue-color light. In addition, the solid-state imaging device alsoincludes an S1 pixel which is provided with an S1 filter with a visiblelight transmittance independent of wavelengths in a visible light regionand has a sensitivity higher than that of the R pixel. On top of that,the solid-state imaging device also includes an S2 pixel which isprovided with an S2 filter with a visible light transmittanceindependent of wavelengths in the visible light region and lower thanthat of the S1 filter and has a sensitivity lower than that of the S1pixel.

In addition, an electronic apparatus provided by embodiments of thepresent invention employs the solid-state imaging device having theconfiguration described above, an optical system for guiding incidentlight to an imaging section employed in the solid-state imaging deviceand a signal processing circuit for processing a signal output by thesolid-state imaging device.

In accordance with embodiments of the present invention, the solid-stateimaging device includes an S1 pixel which is provided with an S1 filterwith a transmittance independent of wavelengths in a visible lightregion and has a sensitivity higher than that of the R pixel. On top ofthat, the solid-state imaging device also includes an S2 pixel which hasa sensitivity lower than that of the S1 pixel. Thus, a solid-stateimaging device having a high sensitivity can be implemented. Inaddition, by providing the RBS1 and RBS2 pixels as described above, onesolid-state imaging device can be used for simultaneously taking twoimages, that is, a low-sensitivity image and a high-sensitivity imagewhich have different levels of brightness. Then, by synthesizing the twoimages, that is, a low-sensitivity image and a high-sensitivity imagewhich have different levels of brightness, it is possible to take animage with a wide dynamic range.

On top of that, the layout of filters can be changed from that of theexisting Bayer array. It is thus possible to eliminate barriers tominiaturization of the solid-state imaging device.

In addition, the electronic apparatus according to the present inventionemploys the solid-state imaging device described above. It is thuspossible to take an image at a high sensitivity and a wide dynamicrange.

In accordance with embodiments of the present invention, it is possibleto provide a solid-state imaging device and an electronic apparatuswhich are capable of keeping up with miniaturizations and taking animage at a high sensitivity and a wide dynamic range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a rough configuration of an embodimentimplementing a solid-state imaging device provided by embodiments of thepresent invention;

FIG. 2 is a diagram showing an embodiment implementing a layout offilters each provided on one of pixels in a pixel section employed inthe solid-state imaging device provided by embodiments of the presentinvention;

FIG. 3 is a diagram showing relations between the wavelength of lightincident on S1 and S2 filters of the solid-state imaging device providedby embodiments of the present invention and the transmittances of thefilters as well as relations between the wavelength of the light and thepixel sensitivity;

FIG. 4 is a diagram showing relations between the quantity of lightincident on each pixel of the solid-state imaging device provided byembodiments of the present invention and the magnitude of a signaloutput by the pixel as well as relations between the saturation pointand the dynamic range;

FIG. 5 is a diagram showing relations between the quantity of lightincident on each pixel of the solid-state imaging device provided byembodiments of the present invention and the magnitude of a signaloutput by the pixel as well as relations between the saturation pointand the dynamic range;

FIG. 6 is a block diagram showing a first embodiment implementing asignal processing circuit employed in the solid-state imaging deviceprovided by embodiments of the present invention;

FIG. 7 is a block diagram showing a second embodiment implementing asignal processing circuit employed in the solid-state imaging deviceprovided by embodiments of the present invention;

FIG. 8 is a block diagram showing a rough configuration of an electronicapparatus provided by embodiments of the present invention; and

FIG. 9 is a diagram showing relations between the quantity of lightincident on each pixel of the existing solid-state imaging device andthe magnitude of a signal output by the pixel as well as relationsbetween the saturation point and the dynamic range.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are explained in chapterswhich are arranged in an order shown below. It is to be noted, however,that implementations of the present invention are by no means limited tothe embodiments.

1: Embodiment of the Solid-State Imaging Device 2: Embodiment of a PixelArray and a Filter Array in the Solid-State Imaging Device 3: Embodimentof Processing of a Signal Output by the Solid-State Imaging Device 4:Other Embodiments of Semiconductor Devices 1: Embodiment of theSolid-State Imaging Device Typical Rough Configuration of theSolid-State Imaging Device

A concrete embodiment of the solid-state imaging device provided by thepresent invention is explained.

FIG. 1 is a block diagram showing a rough configuration of an embodimentimplementing a solid-state imaging device 10 provided by the presentembodiments. A typical example of the solid-state imaging device 10provided by the present embodiments is a solid-state imaging device ofthe MOS (Metal Oxide Semiconductor) type. In the following description,the solid-state imaging device of the MOS type is also referred to as aMOS image sensor.

The solid-state imaging device 10 shown in the block diagram of FIG. 1has a pixel section 13 and a peripheral circuit section. The pixelsection 13 includes a plurality of pixels 12 which are laid outregularly to form a two-dimensional matrix on a substrate such as asilicon substrate. The pixel section 13 is the so-called imaging area.Each of the pixels 12 has a photodiode which serves as anopto-electrical conversion element for converting light incident on thepixel 12 into an electrical signal. In addition to the photodiode, eachof the pixels 12 also includes a plurality of pixel transistors whichare each typically implemented as the so-called MOS transistor.

Typically, each of the pixels 12 can be configured to have three pixelMOS transistors, i. e., a transport transistor, a reset transistor andan amplification transistor. As an alternative, each of the pixels 12can be configured to employ four pixel MOS transistors, i. e., thetransport transistor, the reset transistor, the amplification transistorand a select transistor.

The peripheral circuit section is configured to have a vertical drivingcircuit 14, column-signal processing circuits 15, a horizontal drivingcircuit 16, an output circuit 17 and a control circuit 18.

The control circuit 18 is a circuit for generating clock signals andcontrol signals on the basis of a vertical synchronization clock signal,a horizontal synchronization clock signal and a master clock signal. Thecontrol circuit 18 supplies the clock and control signals to othercircuits such as the vertical driving circuit 14, the column-signalprocessing circuits 15 and the horizontal driving circuit 16.

The vertical driving circuit 14 is typically a shift register. Thevertical driving circuit 14 is a circuit for sequentially scanning thepixel section 13 in the vertical direction in order to select pixels 12in row units. The vertical driving circuit 14 supplies a pixel signal tothe column-signal processing circuit 15 through a vertical signal line19. The pixel signal is based on signal electric charge generated by theopto-electrical conversion element employed in a selected pixel 12 inaccordance with the quantity of light incident on the opto-electricalconversion element.

The column-signal processing circuit 15 is provided typically for everycolumn of the matrix of pixels 12. The column-signal processing circuit15 is a circuit for carrying out signal processing including a processto eliminate noises from a signal output by pixels 12 in accordance witha signal which is output by a black reference pixel for every matrixcolumn. The black reference pixels are pixels created at locationssurrounding the effective pixel area. That is to say, the column-signalprocessing circuit 15 carries out signal processing including a CDS(Correlated Double Sampling) process and signal amplification. The CDSprocess is a process of eliminating fixed pattern noises peculiar to thepixels 12. A horizontal select switch is connected between the outputstage of the column-signal processing circuit 15 and a horizontal signalline 11. It is to be noted that the horizontal select switch itself isnot shown in the block diagram of FIG. 1.

The horizontal driving circuit 16 is typically a shift register too. Thehorizontal driving circuit 16 is a circuit for sequentially outputtinghorizontal scanning pulses for sequentially selecting one of thecolumn-signal processing circuits 15. The horizontal driving circuit 16sequentially outputs pixel signals each generated by the selectedcolumn-signal processing circuit 15 to the horizontal signal line 11.

The output circuit 17 is a circuit for sequentially carrying out signalprocessing on the pixel signals which are each supplied by the selectedcolumn-signal processing circuit 15 to the output circuit 17 through thehorizontal signal line 11.

If the solid-state imaging device 10 described above is used as asolid-state imaging device of the rear surface radiation type, aplurality of wiring layers are not provided on the rear surface on thelight incidence surface side, that is, the so-called light receivingsurface side. Instead, the wiring layers are created on the frontsurface side opposite to the light receiving surface side.

Typical Configurations of a Filter Array and a Pixel Array

Next, the following description explains a layout 20 of filters eachprovided for one of pixels in a pixel section employed in thesolid-state imaging device provided by the present embodiments.

FIG. 2 is a diagram showing an embodiment implementing a layout 20 offilters each provided for one of pixels in a pixel section employed inthe solid-state imaging device provided by the present embodiments.

As shown in the diagram of FIG. 2, an array 20 of filters each providedfor one of pixels in a pixel section employed in the solid-state imagingdevice provided by the present embodiments has four pixels which arelaid out on two rows and two columns. This array of filters eachprovided for one of pixels is repeated throughout the pixel section 13.The four pixels are an S1 pixel 21, an S2 pixel 22, an R pixel 23 and aB pixel 24.

The R pixel 23 has an R filter for transmitting red-color light whereasthe B pixel 24 has a B filter for transmitting blue-color light.

The S1 pixel 21 is provided with an S1 filter with a constanttransmittance which is independent of wavelengths of the light incidenton the S1 filter. On the other hand, the S2 pixel 22 is provided with anS2 filter with a constant transmittance which is independent ofwavelengths of the light incident on the S2 filter and lower than thetransmittance of the S1 filter.

The array 20 shown in the diagram of FIG. 2 is obtained by replacing theG (green) pixels of the GRB (green, red and blue) pixels in the Bayerarray with the S1 pixel 21 and the S2 pixel 22.

The following description explains the characteristic of the S1 filterserving as a filter provided for the S1 pixel 21 and the characteristicof the S2 filter serving as a filter provided for the S2 pixel 22. Thehorizontal axis of the diagram of FIG. 3 represents the wavelength oflight incident on the pixel. The wavelength of light incident on thepixel is expressed in terms of nanometers. On the other hand, thevertical axis of the diagram of FIG. 3 represents the transmittances ofthe S1 and S2 filters provided for the S1 pixel 21 and the S2 pixel 22respectively. In addition, the diagram of FIG. 3 is also a diagramshowing relations between the wavelength of light incident on the S1 andS2 filters provided for respectively the S1 pixel 21 and the S2 pixel 22and the pixel sensitivity for the different transmittances of thefilters. That is to say, a relation between the transmittances of the S1and S2 filters and the wavelength of the incident wavelength is providedfor every pixel sensitivity which is defined as the ratio of themagnitude of a signal generated by a pixel due to a quantity of lightincident on the pixel to the quantity of the light.

In order to make the following explanation simple, the spectralsensitivity characteristic of the solid-state imaging device itself isnot taken into consideration. Since each of the S1 filter and the S2filter transmits incident light for all wavelengths, the sensitivitiesof the S1 pixel 21 and the S2 pixel 22 are the same as thetransmittances of the S1 filter and the S2 filter respectively. Thus, ifthe transmittances of the S1 filter and the S2 filter are 100%, thesensitivities of the S1 pixel 21 and the S2 pixel 22 provided withrespectively the S1 filter and the S2 filter of 100% are also 100%. Inaddition, the sensitivities of the S1 pixel 21 and the S2 pixel 22 are afixed value determined by the transmittances of the S1 filter and the S2filter respectively for all the wavelengths of the light incident on theS1 pixel 21 and the S2 pixel 22 respectively.

By the same token, if the transmittances of the S1 filter and the S2filter are 75%, the sensitivities of the S1 pixel 21 and the S2 pixel 22provided with respectively the S1 filter and the S2 filter of 75% arealso 75%. In the same way, if the transmittances of the S1 filter andthe S2 filter are 50%, the sensitivities of the S1 pixel 21 and the S2pixel 22 provided with respectively the S1 filter and the S2 filter of50% are also 50%. Likewise, if the transmittances of the S1 filter andthe S2 filter are 25%, the sensitivities of the S1 pixel 21 and the S2pixel 22 provided with respectively the S1 filter and the S2 filter of25% are also 25%.

As is obvious from the above description, by adjusting thetransmittances of the S1 filter and the S2 filter are adjusted, each ofthe sensitivities of the S1 pixel 21 and the S2 pixel 22 provided withrespectively the S1 filter and the S2 filter can be set at a desiredvalue. In addition, even if the spectral sensitivity characteristic ofthe solid-state imaging device itself is taken into consideration, thesensitivities of the S1 pixel 21 and the S2 pixel 22 as well as thetransmittances of the S1 filter and the S2 filter can be treated in thesame way as described above with the only exception that thesensitivities of the S1 pixel 21 and the S2 pixel 22 as well as thetransmittances of the S1 filter and the S2 filter are dependent on thewavelength of the light incident on the S1 pixel 21 and the S2 pixel 22respectively.

Each of the S1 filter and the S2 filter transmits light of allwavelengths in the visible light region. The S1 filter and the S2 filterare created on the S1 pixel 21 and the S2 pixel 22 respectively byadoption of typically a vaporization technique applied to a metal havinga metal-film thickness that generates a desired spectrum. Typicalexamples of the metal are the aluminum, the mercury and the rhodium. Asan alternative, a material is made by dispersing carbon black in resinat a concentration generating a desired spectrum and, then, the materialis applied to the S1 pixel 21 and the S2 pixel 22. The R and B filtersare created by adoption of a commonly known technique. To be morespecific, each of the R and B filters is created by applying a materialto the pixel associated with the filter.

If resin containing carbon black is used for creating a filter, theresin is provided with an optical sensitivity characteristic. In thisway, each of the S1 filter and the S2 filter can be created by adoptionof the lithography technique. As a result, a pixel section having theconfiguration described above can be configured with ease by adoption ofa existing technique. Relation between the Quantity of Light Incident ona Pixel and the Output Signal of the Pixel

FIG. 4 is a diagram showing relations between the quantity of lightincident on R, B, S1 and S2 pixels and the magnitude of a signal outputby each of the pixels. In the diagram of FIG. 4, the vertical axisrepresents the magnitude of a signal output by each of the R, B, S1 andS2 pixels whereas the horizontal axis represents the quantity of lightincident on each of the pixels. Thus, each line shown in the diagram ofFIG. 4 represents the relation between the quantity of light incident ona particular one of R, B, S1 and S2 pixels and the magnitude of a signaloutput by the particular pixel.

As described before, the solid-state imaging device employs fourdifferent filters, i. e., the R filter for the R pixel, the B filter forthe B pixel, the S1 filter for the S1 pixel and the S2 filter for the S2pixel.

In such a solid-state imaging device, the transmittance of the S1filter, the transmittance of the R filter and the transmittance of the Bfilter are adjusted so that the sensitivity of the S1 pixel is higherthan the sensitivity of the R pixel. In addition, the transmittance ofthe S2 filter is adjusted so that the sensitivity of the S2 pixel islower than the sensitivity of the S1 pixel.

A dashed line G shown in the diagram of FIG. 4 represents the relationbetween the quantity of light incident on a G (green) pixel in anordinary Bayer array and the magnitude of a signal output by the G pixeldue to the light incident to the G pixel.

As shown in the diagram of FIG. 4, it is desirable to set thesensitivity of the S1 pixel at a value higher than the sensitivity ofthe G pixel but set the sensitivity of the S2 pixel at a value lowerthan the sensitivity of the G pixel.

To put it more concretely, if the sensitivity of a pixel with a filternot absorbing light in the visible light region or a pixel with nofilter is assumed to have a value of 100, the sensitivity of a filterhaving the green filter normally has a value in the range 40 to 60.

That is to say, if the sensitivity of a pixel with a filter notabsorbing light in the visible light region or a pixel with no filter isassumed to have a value of 100, the transmittance of the S1 filter isset at such a value that the sensitivity of the S1 pixel normally has avalue in the range 40 to 100.

Likewise, if the sensitivity of a pixel with a filter not absorbinglight in the visible light region or a pixel with no filter is assumedto have a value of 100, the transmittance of the S2 filter is set atsuch a value that the sensitivity of the S2 pixel normally has a valuewhich is equal to or lower than 60.

By adjusting the transmittance of the S1 filter to such a value that thesensitivity of the S1 pixel is higher than the sensitivity of the Gpixel as shown in the diagram of FIG. 4, it is possible to implement asolid-state imaging device having a sensitivity higher than thesensitivity of a solid-state imaging device which employs G pixels.Thus, in a range of incident light quantities smaller than anincident-light quantity L1 at which the S1 pixel is put at a saturationpoint, the magnitude of a signal output by the S1 pixel at a particularincident light quantity is greater than the magnitude of a signal outputby the ordinary G pixel at the particular incident light quantity. Asshown in the diagram of FIG. 4, however, the dynamic range D1 of the S1pixel is narrower than the dynamic range D of the ordinary G pixel. Bymaking use of a filter having a spectrum with no absorption forwavelengths of incident light as shown in the diagram of FIG. 3 as theS1 filter, however, the sensitivity of the solid-state imaging devicecan be utilized entirely so that the sensitivity of the solid-stateimaging device can be improved.

For the S2 pixel, on the other hand, the S2 pixel is put at thesaturation point at an incident-light quantity L2 which is the upperlimit of a range of incident light quantities not causing the S2 pixelto enter a saturation state. The sensitivity of the S2 pixel is lowerthan the sensitivity of the G pixel however, the incident-light quantityL2 corresponding to the saturation point is greater than theincident-light quantity L at which the ordinary G pixel is put at thesaturation point. That is to say, the dynamic range D2 of the S2 pixelcan be increased to a value greater than the dynamic range D of theordinary G pixel.

If the sensitivity of the S2 pixel is set at a value lower than thehigher sensitivity of the sensitivities of the R and B pixels, thedynamic range D2 of the S2 pixel can be increased to an even largervalue. Unlike the diagram of FIG. 4, however, FIG. 5 shows relations fora case in which the sensitivity of the S2 pixel is set at a value whichis lower than the sensitivity of the R pixel but higher than thesensitivity of the B pixel. In this case, an incident-light quantity L2corresponding to the saturation point in the R pixel can be used as thedynamic range D2 of the R, B and S2 pixels. Thus, the dynamic range D2of the configuration shown in the diagram of FIG. 5 is wider than thedynamic range D2 of the configuration shown in the diagram of FIG. 4.

If the sensitivity of the S2 pixel is set at a value lower than thehigher sensitivity of the sensitivities of the R and B pixels asdescribed above, the incident-light quantity L2 corresponding to thesaturation point and the dynamic range D2 having the incident-lightquantity L2 used as the upper limit thereof are determined by the highersensitivity of the R and B pixels.

It is to be noted that the magnitude relation between the sensitivitiesof the R and B pixels is determined arbitrarily by the spectralsensitivity characteristics of the filters mounted on the image sensorand the spectral sensitivity characteristics of filters other than thefilters mounted on the image sensor. That is to say, the magnituderelation between the sensitivities of the R and B pixels is by no meanslimited to the relations shown in the diagrams of FIGS. 4 and 5 as therelations between the sensitivities of the R and B pixels.

In addition, the sensitivity of the S2 pixel itself can be set at anyvalue as long as the value is lower than the sensitivity of the S1pixel. If the sensitivity of the S2 pixel is set at a value higher thanthe sensitivities of the R and B pixels as is the case with theconfiguration shown in the diagram of FIG. 4, the incident-lightquantity L2 corresponding to the saturation point and the dynamic rangeD2 having the incident-light quantity L2 used as the upper limit thereofare determined by the sensitivity of the S2 pixel. If the sensitivity ofthe S2 pixel is set at a value lower than the higher sensitivity of thesensitivities of the R and B pixels, on the other hand, theincident-light quantity L2 corresponding to the saturation point and thedynamic range D2 having the incident-light quantity L2 used as the upperlimit thereof are determined by the higher sensitivity of the R and Bpixels. That is to say, there is no limitation imposed on the relationbetween the sensitivity of the S2 pixel and the lower sensitivity of thesensitivities of the R and B pixels.

Thus, in a solid-state imaging device employing a pixel section having apixel array including the R, B, S1 and S2 pixels each configured asdescribed above, for incident light quantities smaller than the incidentlight quantity L1 corresponding to the saturation point in the S1 pixel,an image having a high sensitivity can be obtained by synthesizingsignals generated by the S1, R and B pixels. For incident lightquantities larger than the incident light quantity L1, it is possible toobtain an image with a wide dynamic range by synthesizing signalsgenerated by the S2, R and B pixels. First Typical Configuration forImplementing Signal Processing to Generate an Image from Pixel OutputSignals

Next, the following description explains a first embodiment implementinga signal processing circuit 30 for carrying out the signal processingmentioned before in order to generate image luminance signals Y1 and Y2and image color difference signals C1 and C2 from R, B, S1 and S2signals output by pixels. FIG. 6 is a block diagram showing the firstembodiment implementing the signal processing circuit 30 employed in thesolid-state imaging device provided by the present invention. As shownin the figure, the signal processing circuit 30 employs a pixelinterpolation processing section 31, a G processing section 32, a firstMTX processing section 33, a second MTX processing section 34, aS1-pixel saturation determination section 35 and a pixel synthesissection 36.

First of all, the pixel interpolation processing section 31 receives R,B, S1 and S2 signals generated by the R, B, S1 and S2 pixelsrespectively. The pixel interpolation processing section 31 then carriesout a commonly known interpolation process on the R, B, S1 and S2signals generated by the R, B, S1 and S2 pixels respectively in order togenerate a high-sensitivity neutral signal S1, a low-sensitivity neutralsignal S2, a red signal R and a blue signal B which are associated withthe R, B, S1 and S2 pixels respectively.

In the array of the R, B, S1 and S2 pixels, each of the filters for theS1 and S2 pixels has a neutral spectrum which is generated by atransmittance not biased in the visible light region. Thus, bymultiplication of coefficients, handling equivalent to that of signalsoutput by pixels of the same spectrum is possible.

That is to say, as indicated by the graphs shown in the diagram of FIG.3, the transmittance of each of the S1 and S2 filters has a fixed valuerepresenting visible light absorption which is independent of thewavelength of the light. Let notation a1 denote the ratio of thesensitivity of the S1 pixel to the sensitivity of a pixel having afilter not absorbing visible light at all whereas notation a2 denote theratio of the sensitivity of the S2 pixel to the sensitivity of the pixelhaving a filter not absorbing visible light at all. In this case, inaccordance with Eq. (1) given below, a signal that can be processed inthe same way as the low-sensitivity neutral signal S2 can be generatedfrom the high-sensitivity neutral signal S1. By the same token, inaccordance with Eq. (2) given below, a signal that can be processed inthe same way as the high-sensitivity neutral signal S1 can be generatedfrom the low-sensitivity neutral signal S2.

S1=(S2/a2)×a1  (1)

S2=(S1/a1)×a2  (2)

Thus, as shown in the diagram of FIG. 2, there is provided aconfiguration in which S1 and S2 pixels are placed alternately at thelocations of the G pixel in the Bayer array. By virtue of thisconfiguration, it is possible to obtain a resolution equivalent to thatof a case, in which a solid-state imaging device based on the Bayerarray is used, for a range of incident light quantities not greater thanthe incident light quantity L1 while having pixels of four types withspectral characteristics different from each other.

In addition, light hitting the S1 pixel as light with an incident lightquantity greater than the incident light quantity L1 puts the S1 pixelin a saturated state. It is thus necessary to generate thelow-sensitivity neutral signal S2 at the position of the S1 pixel. Thelow-sensitivity neutral signal S2 at the position of the S1 pixel isgenerated by carrying an interpolation process which makes use of asignal generated by the S1 pixel in accordance with Eq. (2) given above.

The S1-pixel saturation determination section 35 produces a result ofdetermination as to whether or not the quantity of the light incident onthe S1 pixel is greater than the incident light quantity L1.

To put it in detail, a signal output by the S1 pixel is supplied to thepixel interpolation processing section 31 as well as the S1-pixelsaturation determination section 35. Then, the S1-pixel saturationdetermination section 35 examines the signal output by the S1 pixel inorder to produce a result of determination as to whether or not thequantity of the light incident on the S1 pixel is greater than theincident light quantity L1 corresponding to the saturation point, thatis, in order to produce a result of determination as to whether or notthe light incident on the S1 pixel has put the S1 pixel at thesaturation point.

If the determination result produced by the S1-pixel saturationdetermination section 35 indicates that the quantity of the lightincident on the S1 pixel is not greater than the incident light quantityL1 corresponding to the saturation point, the S1-pixel saturationdetermination section 35 requests the pixel interpolation processingsection 31 to generate the high-sensitivity neutral signal S1 at theposition of the S2 pixel by making use of a signal generated by the S1pixel. If the determination result produced by the S1-pixel saturationdetermination section 35 indicates that the quantity of the lightincident on the S1 pixel is greater than the incident light quantity L1corresponding to the saturation point, on the other hand, the S1-pixelsaturation determination section 35 requests the pixel interpolationprocessing section 31 to generate the low-sensitivity neutral signal S2at the position of the S1 pixel by making use of a signal generated bythe S2 pixel.

Then, the G processing section 32 generates a green signal G1, a redsignal R1 and a blue signal B1 from the high-sensitivity neutral signalS1, the red signal R and the blue signal B which are received from thepixel interpolation processing section 31. In addition, the G processingsection 32 also generates a green signal G2, a red signal R2 and a bluesignal B2 from the low-sensitivity neutral signal S2 also received fromthe pixel interpolation processing section 31, the red signal R and theblue signal B.

As described earlier, the ratio of the sensitivity of the S1 pixel tothe sensitivity of a pixel having a filter not absorbing visible lightat all is a1 whereas the ratio of the sensitivity of the S2 pixel to thesensitivity of the pixel having a filter not absorbing visible light atall is a2.

In this case, the G processing section 32 generates the green signal G1,the red signal R1 and the blue signal B1, which are signals used forgenerating a high-sensitivity image, from the high-sensitivity neutralsignal S1, the red signal R and the blue signal B by making use of theratio a1 in accordance with Eq. (3) given below. In the same way, the Gprocessing section 32 generates the green signal G2, the red signal R2and the blue signal B2, which are signals used for generating alow-sensitivity image, from the low-sensitivity neutral signal S2, thered signal R and the blue signal B by making use of the ratio a2 inaccordance with Eq. (4) given as follows.

G1=S1−a1(R+B),R1=R,B1=B  (3)

G2=S2−a2(R+B),B2=R,B2=B  (4)

In addition, the G processing section 32 is also capable of generatingthe green signal G1, the red signal R1 and the blue signal B1, which aresignals used for generating a high-sensitivity image, from thehigh-sensitivity neutral signal S1, the red signal R and the blue signalB by making use of the ratio a1 in accordance with Eq. (5) given below.In the same way, the G processing section 32 is also capable ofgenerating the green signal G2, the red signal R2 and the blue signalB2, which are signals used for generating a low-sensitivity image, fromthe low-sensitivity neutral signal S2, the red signal R and the bluesignal B by making use of the ratio a2 in accordance with Eq. (6) givenas follows.

G1=(S1/a1)−(R−B),R1=R,B1=B  (5)

G2=(S2/a2)−(R−B),R2=R,B2=B  (6)

That is to say, the G processing section 32 generates the green signalG1, the red signal R1 and the blue signal B1, which are signals used forgenerating a high-sensitivity image, in accordance with Eq. (3) or Eq.(5). In the same way, the G processing section 32 generates the greensignal G2, the red signal R2 and the blue signal B2, which are signalsused for generating a low-sensitivity image in accordance with Eq. (4)or Eq. (6).

Then, the first MTX processing section 33 carries out matrix processessuch as a white balance process, a linear matrix process and acolor-difference matrix process on the green signal G1, the red signalR1 and the blue signal B1, which are received from the G processingsection 32, in order to generate a high-sensitivity image luminancesignal Y1 and a high-sensitivity image color difference signal C1. Thehigh-sensitivity image luminance signal Y1 and the high-sensitivityimage color difference signal C1 are signals representing ahigh-sensitivity image corresponding to a high illumination side of arange of incident light quantities smaller than the incident lightquantity L1 of light causing the S1 pixel to enter the saturated stateas shown in the diagram of FIG. 4.

By the same token, the second MTX processing section 34 carries outmatrix processes such as the white balance process, the linear matrixprocess and the color-difference matrix process on the green signal G2,the red signal R2 and the blue signal B2, which are received from the Gprocessing section 32, in order to generate a low-sensitivity imageluminance signal Y2 and a low-sensitivity image color difference signalC2. The low-sensitivity image luminance signal Y2 and thelow-sensitivity image color difference signal C2 are signalsrepresenting a low-sensitivity image corresponding to a range ofincident light quantities greater than the incident light quantity L1 ofincident light causing the S1 pixel to enter the saturated state asshown in the diagram of FIG. 4.

Subsequently, the pixel synthesis section 36 synthesizes thehigh-sensitivity image luminance signal Y1 and the high-sensitivityimage color difference signal C1, which have been generated by the firstMTX processing section 33 to serve as signals representing thehigh-sensitivity image, as well as the low-sensitivity image luminancesignal Y2 and the low-sensitivity image color difference signal C2,which have been generated by the second MTX processing section 34 toserve as signals representing the low-sensitivity image, in order togenerate a final image. At that time, if the S1-pixel saturationdetermination section 35 has not detected the saturated state of the S1pixel, the pixel synthesis section 36 generates the final images whichare composed of only high-sensitivity images.

If the S1-pixel saturation determination section 35 has detected thesaturated state of the S1 pixel, on the other hand, for a pixel with theincident light quantity thereof not greater than the incident lightquantity L1, the pixel synthesis section 36 makes use of thehigh-sensitivity image luminance signal Y1 and the high-sensitivityimage color difference signal C1 which represent the high-sensitivityimage of the two images, that is, the low-sensitivity image and thehigh-sensitivity image. For a pixel with the incident light quantitythereof greater than the incident light quantity L1, however, the pixelsynthesis section 36 makes use of the low-sensitivity image luminancesignal Y2 and the low-sensitivity image color difference signal C2 whichrepresent the low-sensitivity image. As described above, by making useof the high-sensitivity image luminance signal Y1 and thehigh-sensitivity image color difference signal C1 for a pixel with theincident light quantity thereof not greater than the incident lightquantity L1, the pixel synthesis section 36 generates the final image asa synthesized image of only high-sensitivity images. By the same token,by making use of the low-sensitivity image luminance signal Y2 and thelow-sensitivity image color difference signal C2 for a pixel with theincident light quantity thereof greater than the incident light quantityL1, the pixel synthesis section 36 generates the final image as asynthesized image of only low-sensitivity images.

If the pixel synthesis section 36 switches the high-sensitivity imageluminance signal and the high-sensitivity image color difference signalfrom the high-sensitivity image luminance signal Y1 and thehigh-sensitivity image color difference signal C1 for a pixel with theincident light quantity thereof not greater than the incident lightquantity L1 to the low-sensitivity image luminance signal Y2 and thelow-sensitivity image color difference signal C2 for a pixel with theincident light quantity thereof greater than the incident light quantityL1 or vice versa, the synthesized image undesirably becomes unnatural.In order to solve this problem, one of a variety of commonly knownmethods is selected to serve as a method for generating a natural image.For example, the synthesis ratio of signals representing images beingsynthesized is changed to a value according to the incident lightquantity. Second Typical Configuration for Implementing SignalProcessing to Generate an Image From Pixel Output Signals

Next, the following description explains a second embodimentimplementing a signal processing circuit 40 for carrying out signalprocessing mentioned before in order to generate an image luminancesignal Y and an image color difference signal C from signals output bypixels. FIG. 7 is a block diagram showing the second embodimentimplementing the signal processing circuit 40 employed in thesolid-state imaging device provided by the present embodiments. As shownin the figure, the signal processing circuit 40 employs a pixelinterpolation processing section 41, an S1-pixel saturationdetermination section 42, an S processing section 43, a G processingsection 44 and an MTX processing section 45.

First of all, in the same way as the first embodiment implementing thesignal processing circuit 30 as described above, the pixel interpolationprocessing section 41 receives R, B, S1 and S2 signals generated by theR, B, S1 and S2 pixels respectively. The pixel interpolation processingsection 41 then carries out a commonly known interpolation process onthe R, B, S1 and S2 signals generated by the R, B, S1 and S2 pixelsrespectively in order to generate a high-sensitivity neutral signal S1,a low-sensitivity neutral signal S2, a red signal R and a blue signal Bwhich are associated with the R, B, S1 and S2 pixels respectively. Thepixel interpolation processing section 41 employed in the signalprocessing apparatus according to the second embodiment may carry outthe commonly known interpolation process on the R, B, S1 and S2 signalsgenerated by the R, B, S1 and S2 pixels respectively in order togenerate a high-sensitivity neutral signal S1, a low-sensitivity neutralsignal S2, a red signal R and a blue signal B which are associated withthe R, B, S1 and S2 pixels respectively in the same way as the signalprocessing apparatus 30 according to the first embodiment.

Also in the same way as the signal processing apparatus 30 according tothe first embodiment, the S1-pixel saturation determination section 42produces a result of determination as to whether or not the quantity ofthe incident light is greater than the incident light quantity L1. Ifthe determination result produced by the S1-pixel saturationdetermination section 42 indicates that the quantity of the lightincident on the S1 pixel is greater than the incident light quantity L1corresponding to the saturation point, the S1-pixel saturationdetermination section 42 requests the pixel interpolation processingsection 41 to carry out an interpolation process of generating thelow-sensitivity neutral signal S2 at the position of the S1 pixel bymaking use of a signal generated by the S2 pixel.

Then, the S processing section 43 synthesizes the high-sensitivityneutral signal S1 generated by the pixel interpolation processingsection 41 and the low-sensitivity neutral signal S2 also supplied bythe pixel interpolation processing section 41 in order to generate asynthesized neutral signal S.

At that time, for every pixel, the S1-pixel saturation determinationsection 42 produces a result of determination as to whether thehigh-sensitivity neutral signal S1 or the low-sensitivity neutral signalS2 is to be used in the synthesis process.

To put it in detail, for an S1 pixel with the incident light quantitythereof smaller than the incident light quantity L1, that is, for an S1pixel not put in the saturated state, the high-sensitivity neutralsignal S1 is used in the synthesis process. For an S1 pixel with theincident light quantity thereof greater than the incident light quantityL1, that is, for an S1 pixel put in the saturated state, on the otherhand, the low-sensitivity neutral signal S2 is used in the synthesisprocess. For an S1 pixel with the incident light quantity thereof in arange in close proximity to the incident light quantity L1, a ratioprovided for the incident light quantity to serve as the synthesis ratioof the high-sensitivity neutral signal S1 to the low-sensitivity neutralsignal S2 is properly determined in order to generate a more naturalsynthesized image.

Then, the G processing section 44 generates a green signal G3, a redsignal R3 and a blue signal B3 from the neutral signal S generated bythe S processing section 43 as well as the red signal R and the bluesignal B which are generated by the pixel interpolation processingsection 41.

To put it in detail, the G processing section 44 generates the greensignal G3, the red signal R3 and the blue signal B3 in accordance withEq. (7) or Eq. (8) given below. In these equations, notation a1 denotesthe ratio of the sensitivity of the S1 pixel to the sensitivity of apixel having a filter not absorbing visible light at all.

G3=S−a1(R+B),R3=R,B3=B  (7)

G3=S3/a1−(R+B)R3=R,B3=8  (8)

Then, the MTX processing section 45 carries out matrix processes such asa white balance process, a linear matrix process and a color-differencematrix process on the green signal G3, the red signal R3 and the bluesignal B3, which are received from the G processing section 44, in orderto generate an image luminance signal Y and an image color differencesignal C.

If the incident light quantity is small, a signal output by the S1 pixelis processed to generate a high-sensitivity image. In addition, bymaking use of the S2 pixel having a low sensitivity, the dynamic rangecan be widened to the incident light quantity L2 at which the S2 pixelis put at the saturation point. In this way, even if the quantity of theincident light puts the S1 pixel at the saturation point, the S2 pixelhaving the S2 filter does not enter the saturated state. By synthesizingsignals output by the S1 and S2 pixels through adoption of the methoddescribed earlier, it is possible to find an image luminance signal Yand an image color difference signal C which represent one synthesizedimage.

Since both the S1 and S2 filters provided on the S1 and S2 pixelsrespectively transmit light of all wavelengths, by multiplication of thecoefficients a1 and a2, handling equivalent to that of a signal from apixel of the same spectrum is possible.

For the reason described above, by alternately placing the S1 and S2pixels at typically the locations of the G pixels in the Bayer array asshown in the diagram of FIG. 2, it is possible to obtain a resolutionequivalent to that of a case, in which a solid-state imaging devicebased on the Bayer array is used, while having pixels of four types withspectral characteristics different from each other.

In addition, by providing the S1 and S2 pixels, it is possible to obtaina high-sensitivity image and a low-sensitivity image without reducingthe resolution to a level lower than that of a solid-state imagingdevice which employs the existing Bayer arrays. On top of that, it ispossible to implement a solid-state imaging device capable of providingboth a high sensitivity and a wide dynamic range and implement a camerasystem employing such a solid-state imaging device.

3: Typical Configurations of Electronic Apparatus

The solid-state imaging devices according to the present invention canbe employed in electronic apparatus such as a camera and a portableapparatus having an embedded camera. That is to say, it is possible toimplement electronic apparatus such as a camera employing thesolid-state imaging device, a portable apparatus having an embeddedcamera employing the solid-state imaging device and other electronicapparatus employing the solid-state imaging device.

FIG. 8 is a block diagram showing a rough configuration of an electronicapparatus provided by the present invention. To be more specific, FIG. 8is a block diagram showing a rough configuration of a digital stillcamera 50 which is capable of taking a still image by virtue of asolid-state imaging device 52 employed in the digital still camera.

As shown in the block diagram, the digital still camera 50 employs anoptical lens 51, the solid-state imaging device 52, a signal processingcircuit 53 and a driving circuit 54. The optical lens 51 serves as anoptical system in the camera 50.

The solid-state imaging device 52 is the solid-state imaging deviceprovided by the present invention as described so far. The optical lens51 is an optical system for creating an image on an image creationsurface in the solid-state imaging device 52 on the basis of image lightwhich comes from an object of photographing to serve as incident light.Thus, during a certain period, signal charge is accumulated in anopto-electrical conversion element which is employed in the solid-stateimaging device 52. The driving circuit 54 is a section for supplying atransfer operation signal also referred to as a driving signal or atiming signal to the solid-state imaging device 52. The driving signalgenerated by the driving circuit 54 transfers a signal output by theopto-electrical conversion element employed in the solid-state imagingdevice 52 to the signal processing circuit 53. The signal processingcircuit 53 is a section for carrying out various kinds of signalprocessing on the signal output by the opto-electrical conversionelement employed in the solid-state imaging device 52. The signalprocessing circuit 53 is typically the signal processing circuit 30shown in the block diagram of FIG. 6 or the signal processing circuit 40shown in the block diagram of FIG. 7. A signal generated by the signalprocessing circuit 53 as a result of the signal processing is stored ina storage medium such as a memory and output to typically a monitor.Embodiments implementing the digital still camera 50 include a cameramodule in which each of the optical lens 51, the solid-state imagingdevice 52, the signal processing circuit 53 and the driving circuit 54is modularized.

The present invention can be applied to a portable apparatus having anembedded camera such as the digital still camera 50 shown in the blockdiagram of FIG. 8 or the camera module described above. A representativeexample of the portable apparatus is a portable phone.

In addition, the configuration shown in the block diagram of FIG. 8 canbe implemented as the so-called imaging function module. In the case ofthe digital still camera 50 shown in the block diagram of FIG. 8, theso-called imaging function module is a module in which each of theoptical lens 51, the solid-state imaging device 52, the signalprocessing circuit 53 and the driving circuit 54 is modularized toimplement imaging functions. That is to say, the present embodiments canbe applied to an electronic apparatus which employs such an imagingfunction module.

In the embodiments described so far, a CMOS image sensor is implementedto serve as a typical solid-state imaging device. It is to be noted,however, that the present embodiments can also be applied to asolid-state imaging device other than the CMOS image sensor. Forexample, the present embodiments can also be applied to a solid-stateimaging device which is implemented by modifying a color filter arrayemployed in a general-purpose solid-state imaging device. In this case,the general-purpose solid-state imaging device can be any other imagesensor such as a CCD (Charge Coupled Device) image sensor or a CMD(Charge Modulation Device) image sensor. That is to say, the imagingmethod is not taken into consideration.

In addition, the range of systems to which the present embodiments areapplied is by no means limited to the camera system such as a stillpicture camera or a moving picture camera.

It is also worth noting that the scope of the present invention is by nomeans limited to the configurations of the embodiments described so far.That is to say, the configurations of the embodiments can be changed toa variety of modified versions within a range which does not deviatefrom essentials of the present invention.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2009-214819 filedin the Japan Patent Office on Sep. 16, 2009, the entire content of whichis hereby incorporated by reference.

The invention claimed is: 1.-7. (canceled)
 8. A solid-state imagingdevice comprising: a pixel unit configured to have a plurality of pixelgroups, each of the pixel groups having four pixels which are laid outon two rows and two columns; and wherein a first pixel of the fourpixels transmits all wavelengths of incident light and a second pixel ofthe four pixels transmits a part of the all wavelengths of the incidentlight; and wherein an another pixel signal is generated by at least twoof four pixels.
 9. The solid-state imaging device according to claim 8,further wherein a third pixel is one of the four pixels and has adifferent transmittance than a transmittance of the first pixel.
 10. Thesolid-state imaging device according to claim 9, wherein a sensitivityof the first pixel is higher than that of the third pixel.
 11. Thesolid-state imaging device according to claim 9, wherein the third pixeltransmits all wavelengths of the incident light.
 12. The solid-stateimaging device according to claim 8, wherein a fourth pixel is one ofthe four pixels and has a transmittance that is different than atransmittance of the second pixel.
 13. The solid-state imaging deviceaccording to claim 8, wherein a color transmittance of the another pixelis different from that of the four pixels.
 14. The solid-state imagingdevice according to claim 8, wherein the another pixel is a green pixel.15. The solid-state imaging device according to claim 8 wherein thesensitivity of the first pixel has a value in the range 40 to 100 wherethe sensitivity of a pixel having no filter is
 100. 16. The solid-stateimaging device according to claim 8 wherein the sensitivity of the thirdpixel is not greater than 60 where the sensitivity of a pixel having nofilter is
 100. 17. The solid-state imaging device according to claim 8wherein the sensitivity of the third pixel is set at a value lower thanthe higher sensitivity of the sensitivities of the second and the forthpixels.
 18. The solid-state imaging device according to claim 8 wherein:an image luminance signal is generated by making use of signals outputfrom the first and the third pixels, that is, said image luminancesignal is generated from the first pixel in an illumination range withan upper limit thereof causing saturation of the first pixel whereassaid image luminance signal is generated from the third pixel in anillumination range with a lower limit thereof causing said saturation ofthe first pixel; and one image is generated by synthesizing said imageluminance signal generated from the first pixel with said imageluminance signal generated from the third pixel.
 19. The solid-stateimaging device according to claim 8 wherein: an image luminance signalis generated by making use of signals output by the first, the second,the third and the forth pixels; and a green signal is generated bymaking use of a ratio of said signal output by the first pixel to asignal output by a pixel having a filter absorbing no light in a visiblelight region or a ratio of said signal output by the third pixel to saidsignal output by said pixel having said filter absorbing no light insaid visible light region from said signals output by the first, thesecond and the forth pixels or from said signals output by the second,the third and the forth pixels.